Satellites in geostationary orbits (GSOs) have been widely preferred for several decades because of the economic advantages afforded by such orbits. In a geostationary orbit, a satellite traveling above the Earth's equator, in the same direction as that in which the Earth is rotating, and at the same angular velocity, appears stationary relative to a point on the Earth. These satellites are always "in view" at all locations within their service areas, so their utilization efficiency is effectively 100 percent. Antennas at Earth ground stations need be aimed at a GSO satellite only once; no tracking system is required.
Coordination between GSO's and with terrestrial services is facilitated by governmental allocation of designated "slots" angularly spaced according to service type. Given the desirability of geostationary satellite orbits and the fact that there are only a finite number of available "slots" in the geostationary "belt," the latter capacity has been essentially saturated with satellites operating in desirable frequency bands up through the Ku-band (up to 18 GHz). As a result, the government has been auctioning the increasingly scarce remaining slots.
This has encouraged the development of complex and expensive new systems including those using low Earth orbits (LEO's), medium Earth orbits (MEO's), and higher frequencies, for example, the Ka band (up to approximately 40 GHz). Growth to higher frequencies is limited by problems of technology and propagation, and expansion in satellite applications requires exploitation of the spatial dimension (i.e., above and below the GSO belt). A host of proposed LEO and MEO systems exemplify this direction.
The recently filed LEO and MEO system applications, however, introduce another problem. Frequency coordination and sharing are made difficult by the unstructured criss-crossing of the lines of sight of these systems. This has the potential of severely impeding effective spectrum use with nongeostationary orbits (NGSO) in general.
There has been no known prior effort to exploit coordinatable systems of inclined eccentric geosynchronous orbits (IEGOs) in a systematic manner, even though the unused domain of inclined eccentric geosynchronous orbits offers great potential for the coordinatable growth of satellite service.
In the parent application, U.S. Ser. No. 08/876,278, clusters of inclined eccentric geosynchronous orbits operate above and below the GSO belt. As the satellites in the parent application approach the alignment with the GSO belt, satellite operation must be discontinued because the line of sight with the GSO belt may overlap. As the satellites travel into the lower portion of their paths, contact with a ground station in the northern hemisphere is not possible. Thus, either service is discontinued or service is handed over to another satellite orbitally out of phase with the satellite out of contact.
While the various prior systems function relatively satisfactorily and efficiently, none discloses the advantages of the coordinatable system of inclined, eccentric geosynchronous satellite orbits in accordance with the present invention as is hereinafter more fully described.